1. Field of the Invention
The present invention relates to a storage medium having stored therein an image processing program, an image processing apparatus, an image processing system, and an image processing method, and more particularly to a storage medium having stored therein an image processing program for displaying an image obtained by combining a real world image with a virtual world image, an image processing apparatus, an image processing system, and an image processing method.
2. Description of the Background Art
Conventionally, in the field of Augmented Reality (AR), which is a technology of additionally displaying in a taken image of a real space various kinds of information such as letters or virtual objects generated by a computer, methods have been studied for determining a reference coordinate system for displaying the virtual objects, as an interactive interface between a real space and the computer. For example, in “An Augmented Reality System and its Calibration based on Marker Tracking” by Hirokazu Kato, Mark Billinghurst, Koichi Asano, and Keihachiro Tachibana, Transactions of the Virtual Reality Society of Japan, Vol. 4, No. 4, 1999, pp. 607-616 (hereinafter referred to as Non-Patent Document 1), a method of calculating, based on the position and the orientation of a marker in an image taken by a camera, a relative position and a relative orientation between the marker and the camera in the real world (see Non-Patent Document 1, for example).
However, in the method described in Non-Patent Document 1, a virtual object or the like additionally displayed in a taken image of the real space can be moved only by moving the viewpoint by moving the camera. Therefore, the user cannot perform operations on the virtual object or the like. Moreover, in order to cause the user's own viewpoint to be directed to the contents of the taken image, the user has to hold or wear an imaging apparatus for taking an image of the real world. In a case where the user performs an input operation by using his/her fingers on the imaging apparatus which the user is holding or wearing, it is difficult for the user to perform such an input operation while taking an image, due to physical restriction. Accordingly, such a conventional input method used in the field of Augmented Reality has a low interactiveness between the real world and the Augmented Reality, and lacks in interest and operability, due to a small variation of contents which can be inputted by the user.